Method of and apparatus for forming grid electrodes



Feb. 21, B LLANT NE METHOD OF AND APPARATUS FOR FORMING GRID ELECTRODES Filed June 16, 1931- Patented Feb. 21, 1933 UNITED STATES PA'TENT OFFICE I STUART BALLANTINE, OF MOUNTAIN LAKES, NEW JERSEY, ASSIGNOR TO RADIO COR- PORATION OF AMERICA, A CORPORATION OF DELAWARE METHOD OF AND APPARATUS FOR FORMING- GRID ELECTRODES Application filed June 16,

tubes having the operating characteristics described in the Proceedings of the Institute of Radio Engineers, December, 1930, pages 2102 to 2127 have employed control grid windings of variable diameter and/or pitch, as well as windings. of uniform pitch from which one or more turns were removed. 7 According to the present invention, grids of the type employed in poly-mu tubes are prepared byfirst forming the grid as a helical winding, preferably of constant pitch, and

then bending one or more of the turns out of the helical surface. I

.Objects of the invention are to provide methods of and apparatus for forming grid electrodes by the deformation of a helical grid winding. F urther objects are to provide a method and apparatus of the type stated in which the deformation is effected by forcing one or more wedge shaped blades into or through parts of the helical grid winding, thereby bending some of the turns aside.

These and other objects of the invention will be apparent from the following specification, when taken with the accompanying drawing, in which:

Fig. 1 is a perspective view illustrative of the invention; the grid and presser bars being shown in their relative positions prior to the deformation of the grid winding; I

Figs. 2 and 3 are fragmentary longitudinal sections showing, respectively, presser. bars fully entered into, and withdrawn from, the

1 g Figs. 4, 5 and 6 are front, end and top views, respectively, of one form of apparatus suitable for forming the grids;

apart by a spring 9. As best shown in the bars 3 and 3 are inclined in opposite di- 1931. Serial No. 544,801.

Figs. 7 and 8 are end and top views of another embodiment; and FFig. 9 is asection taken on line 9'9 of The grid'shown in Fig. 1 is of the type employed in many styles of vacuum tubes now manufactured commercially, and consists of a pair of supporting wires 1 upon which a finer wire 2 is wound as a helix of uniform pitch. Both hand-operated and automatic machines for winding such grids and for welding the, helical winding 2 to the supporting wires 1 are 'wellknown in the industry.

According to the present invention, a helical grid winding of this known type may be given a desired-form for inclusion in a polymu tube ,byreforming some of the turns of the helix by spreader bars 3 that are forced between adjacent turns of the winding to bend a plurality of turns, or fractional turns .of the winding, axially of the grid.

As shown in Fig. 2, oppositely disposed Spreader bars 3, 3 have been moved into the Winding to bend aside a plurality of turns at each side of the spreader bars. Upon removal of the spreader bars, as shown in Fig. 3, the resiliency of the winding 2 permits the bent turns to spring back to some extent. In

the design of apparatus for shaping the grids,

1 may be. placed, the frame having perfora-' tions 6 for receiving the ends of wires 1 which project beyond the helical winding 2. Upper and lower sets of spreader blades 3, 3 are carried by a pair of levers 7 which'are pivoted upon a shaft 8 and normall held ig. 6,

rections to permit the spreader bars to slide between adjacent turns of the winding. The parts of the apparatus are so proportioned that, when the grid is slid as far as possible upon the mandrel 5, the spreader bars are then slipped upon the mandrel 5 of the formmg machine, with the end turn of the winding 2 resting against the face of the frame 4;, or with the ends of supporting wires 1 seated against the ends of perforations 6. The operator presses the lever 7 together to force the spreader blades 3, 3' into the winding and, upon releasing the pressure, the levers open to permit removal of the finished In place of moving the edges of the spreader blades radially of the wind, these edges may move along chords of the winding to bend the turns axially of the grid. One form of apparatus employing this method is illustrated in Figs. 7 to 9, inclusive. The apparatus includes a suitable base or supporting structure 10 for the post 11 which carrles a mandrel 12 for receiving the grid blanks. Recesses 13 are provided in the post 11 for receiving the ends of the supporting wires 1 of the grid blanks. The spreader blades 14: project downwardly from a slider 15 which has a dove-tail engaging a correspondingly shaped slideway 16 on the post 11.

To shape a grid, the operator raises the slider 15, slips a grid blank upon the mandrel 12 and depresses the slider to force the knifeshaped spreader bars 14 through the helical grid winding. In Figs. 7 and 9, the dotted lines 2 indicate the position of the helical winding when the grid blank is placed on the mandrel. If desired, spring means may be provided for normally holding the slider 15 in raised position but the slider 15 is of such small size and light weight that no dificulty or delay is experienced when it is raised manually.

Apparatus such as shown in Figs. 4 5 and 6 may be provided with interchangeable levers- 7 which carry various styles and arrangements of spreader blades. Different combinations of such levers may then be employed to obtain final grid structures of substantially different forms and electrical properties. Interchangeable slides provided with different combinations of spreader blades may be provided for the other type of bending machine.

While I have illustrated but one form of grid electrode having bent turns, it will be 1 claim: I J

1. The process of forming a vacuum tube grid which comprises the steps of first forming a helical winding and securing each winding thereof to supporting wires, and then forcing a spreading tool between adjacent turns of said winding to deflect portions thereof axially of the grid structure while maintaining the contacts between the grid wire and the supporting means fixed.

2. Apparatus for forming grids, comprising a support for holding a grid blank in the form of a helical winding, means cooperating with said support 'to insure a predetermined positioning of a grid upon said support, and a spreader blade movable with respect to said support and along such path that said blade will enter between adjacent turns of a grid ed on said frame, and a. spreader blade on said lever, said blade being adapted to slide between ajacent turns of a grid blank mounted on said mandrel.

5. The invention as set forth in claim 3, wherein said supporting means comprises a slider carrying said spreader blades, and a slideway on said frame, said slider being movable upon said slideway.

6. In the art of forming vacuum tube grids wherein a grid wire is wound in the form of a helix and secured to a supporting wire at a point in each turn of the helix, the method of changing the characteristics of the grid after it is wound and attached to the supporting wire which comprises applying pressure between adjacent turns of the helical winding at unsecured points thereof to bend the grid wire at the points of support and thereby displace portions of the helical winding axially of the grid structure while maintaining the points of support of the grid wire on the supporting wire intact.

7. In the art of forming vacuum tube grids wherein a grid wire is wound in the form of a helix and secured to a supporting wire at a point in each turn of the helix, the method of changing'the characteristics of the grid after it is wound and attached to the supporting wire which comprises, s reading the wound structure intermediate t e points of support so as to maintain uniform'density of windings per unit length at the points of support and non-uniform density ofwindmgs per umt length at unsupported points along certain portions of the grid structure.

8. The method of changing the characteristics of a vacuum tube having a cathode and anode between which is a grid structure formed from a multi-turn helical winding attached at diametrically opposite points in each turn of the helix to supporting means which comprises spreading certain adjacent turns of the helix at points intermediate each support point thereof so thatthe turns are distorted from the position of windin and utilizing the resilience of the material to maintain after spreading a variable concentration of helical turns per unit axial length thereof so that when signals are applied between the grid and cathode electrodes the electron flow toward the anode varies throughout the length of the grid in accordance with the concentration of the helical turns.

9. The method of converting a grid structure which has been formed by winding grid wire into a helix of substantially constant pitch about a support means and in which each turn is fixed to the support means, for use in a poly-mu tube which comprises displacing portions of the helical windings at unsupported points so as to maintain substantially uniform density of windings per unit length axially alon the points of support and non-uniform ensity' of windings per unit length at other points of said wind- 1 mgs.

STUART BALLANTINE. 

